Trigger mechanism for firearms with self-loading actions

ABSTRACT

The trigger mechanism allows the firearm to operate in a closed-bolt mode during semi-automatic fire and in an open-bolt mode during automatic fire. The mode change occurs only after the first round is discharged after the selector has been moved instead of when the selector switch is moved, thus avoiding undesirable mechanism noise or motion at the time of selecting the firing mode.

REFERENCE TO RELATED APPLICATION

This is a formal application based on and claiming the benefit of United States provisional patent application no. 60/713,722, filed Sep. 6, 2005.

BACKGROUND OF THE INVENTION

This invention relates to firearms and weapons in general and in particular to a trigger mechanism particularly intended for firearms with self-loading actions.

Self-loading actions are those where the next round loads after a round has been discharged, whether semi-automatic or automatic. Once the firearm is cocked, the operator must only pull the trigger to fire a round and load the next available round from a magazine, belt or other storage device. As long as there is ammunition available the firearm will be ready to fire the next time the operator pulls the trigger.

Self-loading firearms operate either in open-bolt or closed-bolt fashion. This refers to the position of the bolt and carrier. The bolt houses the firing pin and locks together with the barrel during firing. It is responsible for holding the case of the bullet in the chamber of the barrel and withstand the considerable pressure and recoil that occur. The carrier holds, guides and locks/unlocks the bolt from the barrel. It is the motion of the bolt and carrier, as a result of expanding gas from the fired bullet, that causes the firing mechanism to be reset and the next round to be loaded from the magazine into the ready to fire position.

Typically a closed-bolt rifle is more accurate than an open-bolt rifle. The drawback of a closed-bolt rifle is the occurrence of “cook-off” under extended heavy rates of fire. “Cook-off” is the condition where the heat of the barrel and chamber of the rifle initiate the next loaded round without the trigger being pulled. This is a dangerous condition where the rifle may fire without the intent of the operator. An open-bolt rifle avoids this, and thus can operate at prolonged higher rates of fire.

In the prior art, at least one mechanism allows the firearm to operate in a closed-bolt mode or open-bolt mode. However, while switching from open-bolt mode (automatic) to closed-bolt mode, there is a loud mechanical motion of the carrier to the closed-bolt position. This noise and motion is considered undesirable from the operator's standpoint in terms of sound signature while trying to maintain stealth, and potential surprise/confusion over the motion of the carrier.

SUMMARY OF THE INVENTION

The invention provides a novel trigger mechanism incorporating unique fire control logic. “Logic” in this context refers to the behavior of the weapon depending on various conditions, or more specifically, the chain of events that comprise a full cycle of the weapon from pulled trigger through to the home position.

One aspect of the invention is that it allows the firearm to operate in a closed-bolt mode during semi-automatic fire (when accuracy is desirable) and operate in an open-bolt mode (when high heat conditions exist) to avoid possible cook-offs. The mode change occurs when the first round is discharged after the selector has been moved instead of when the selector switch is moved, and thus there is no undesirable noise or motion as in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference to the accompanying drawings of a preferred embodiment of the trigger mechanism, in which:

FIG. 1 is a cut-open perspective view of relevant portions of a representative rifle embodying the trigger mechanism, with the rifle barrel, gas chamber, firing pin and other typical components removed for clarity;

FIG. 2 is a generally corresponding cut-open side view;

FIG. 3 is a generally corresponding exploded perspective view;

FIG. 4 is a perspective view of the auto-sear;

FIGS. 5A and 5B are opposite side perspective views of the hammer,

FIGS. 6A and 6B are lower and upper perspective views of the trigger;

FIG. 7 is a perspective view of the disconnect;

FIG. 8 is a perspective view of the disconnect in combination with the trigger;

FIG. 9 is a perspective view of the carrier sear;

FIGS. 10A and 10B are upper and lower perspective views of the auto-sear;

FIG. 11 is a cross-section showing the safety sear and carrier sear together;

FIGS. 12A, 12B and 12C are various perspective views of the auto-disconnect;

FIG. 13 is a perspective view of the selector;

FIG. 14A is a side view of the selector, and FIGS. 14B-D are various cross-sectional views thereof;

FIG. 15 shows the primary components for closed-bolt operation, and the home position of the closed-bolt operating cycle;

FIG. 16 shows Step 1 of the closed-bolt operating cycle;

FIG. 17 shows Step 2 of the closed-bolt operating cycle;

FIG. 18 shows Step 3 of the closed-bolt operating cycle;

FIG. 19 shows Step 4 of the closed-bolt operating cycle;

FIG. 20 shows Step 5 of the closed-bolt operating cycle (the home position again);

FIG. 21 shows Step 1 of the open-bolt operating cycle;

FIG. 22 shows Step 2 of the open-bolt operating cycle;

FIG. 23 shows Step 3 of the open-bolt operating cycle;

FIG. 24 shows Step 4 of the open-bolt operating cycle;

FIG. 25 shows the selector moved from the automatic mode (open-bolt operation) to the semi-automatic mode (closed-bolt operation), to begin the transition from open-bolt to closed-bolt;

FIG. 26 shows the trigger depressed, initiating a semi-automatic cycle from automatic mode;

FIG. 27 shows the safety sear and carrier sear held down and away from the carrier when the trigger is released, after one round has been fired, so that the firearm is now in the closed-bolt configuration;

FIG. 28 shows the selector moved from the semi-automatic mode (closed-bolt operation to the automatic mode (open-bolt operation), to begin the transition from closed-bolt to open-bolt; and

FIG. 29 shows the weapon part way through the automatic cycle, with the trigger remaining depressed and the firearm therefore continuing to cycle until the trigger is released or ammunition is depleted.

DETAILED DESCRIPTION

Referring now to the accompanying drawings, the preferred embodiment will be described in detail. It should be understood that this is an example of the invention only, and that other embodiments and variations are possible within the scope of the invention.

FIGS. 1-3 show the primary components of the trigger mechanism, embodied in a rifle 1. For simplicity, many conventional elements of the rifle are not illustrated, other than the receiver 2, grip 3, trigger guard 4, and carrier 5. The main components for operation of the invention are the auto-sear 6, the hammer 7, the trigger 8, the disconnect 9, the carrier sear 10, the safety sear 11, the auto-disconnect 12, and the selector 13.

The preceding main components of the preferred embodiment will be described first, followed by a description of closed-bolt operation, then open-bolt operation, then the mechanism which integrates the two modes of operation and permits switching between them.

Components of the Preferred Embodiment

Auto-Sear

FIG. 4 shows the auto-sear 6. The purpose of the auto-sear is to prevent the hammer from moving unless the carrier is in its fully forward position. The auto-sear is acted on in a clockwise direction by a spring 19, so that surface 18 engages a notch 25 in the hammer unless rotated by the carrier. Thus a round cannot be fired unless the bolt is locked with the barrel. In fully automatic mode, the auto-sear is the only element preventing the hammer from moving while the trigger is depressed, i.e. it is the mechanism that releases the hammer and once the carrier is fully forward, to fire the round.

The auto-sear pivots around a pivot axis 15, provided by a auto-sear pin 16 in the receiver 2 (see FIGS. 1-3). The carrier 5 contacts the surface 17 and rotates the auto-sear forward (counter-clockwise when viewed from the left side as in FIG. 2), disengaging it from the hammer. Until the auto-sear is so rotated by the carrier, the surface 18 sears with a notch in the hammer, blocking rotation of the hammer.

Hammer

FIGS. 5A and 5B show the hammer 7. The hammer rotates on a hammer pin 20 mounted in the receiver and so that surface 21 strikes the firing pin, transferring energy stored in the hammer spring 22 (see FIGS. 2 and 3) to the firing pin with sufficient energy to initiate the primer in the ammunition, thus firing the round.

The carrier also pushes back against surface 21 as it moves backwards, to reset the hammer against the hammer spring. Surface 23 sears with the disconnect to interrupt the semi-automatic cycle after one round while the trigger remains pulled. (The disconnect is cammed out of interference in full automatic mode and thus does not engage this surface and allows the cycle to continue.) Surface 24 engages the trigger. The trigger interferes with the rotation of the hammer by engaging this notch when the trigger is not pulled. The auto-sear engages surface 25. When the carrier is not in the fully forward position, the auto-sear is able to interfere with the rotation of the hammer by engaging this notch. The hammer is acted on in a counter-clockwise direction by a spring.

Trigger

FIGS. 6A and 6B show the trigger 8. The trigger of course controls the selected firing cycle of the weapon. It interferes with the motion of the hammer when not depressed. In automatic mode it provides the pivotal input to move the carrier sear to disengage it from the carrier. The trigger also provides a support for the disconnect which limits the semi-automatic cycle to one round only per depression of the trigger.

While in safe mode the movement of the trigger is prohibited. Immobilizing the trigger either by selecting the safe mode or by the default function of a grip safety (not shown), prevents the weapon from being able to cycle.

The trigger rotates on trigger pin 31. The operator's finger pulls on surface 32 to fire the weapon. The edge 33 sears with the hammer. It engages a notch in the hammer interfering with its ability to rotate. The surface 34 is cut away to allow retention of the pivot axis pin by means of a spring wire engaging a groove in the pin. The surface 35 acts against the safety sear/carrier sear sub-assembly to disengage the sears from the carrier during automatic mode open-bolt operation. The pocket 36 exists for a spring to provide a separating force between the trigger and disconnect. The slot 37 houses and aligns the disconnect.

Disconnect

FIG. 7 shows the disconnect 9, and FIG. 8 shows the disconnect in combination with the trigger 8.

The purpose of the disconnect 9 is to interrupt the firing cycle to allow only one round to be fired in semi-automatic mode. While the trigger is depressed, the disconnect is presented in interference to the hammer. Since the disconnect is spring loaded with respect to the trigger, the hammer pushes the disconnect out of the way as the carrier pushes the hammer back, resetting the mechanism. As the hammer reaches the fully reset position the disconnect engages the hammer, preventing it from moving forward As the trigger is released the disconnect releases the hammer but not prior to the trigger engaging the hammer and thus preventing the weapon from firing. This is the fundamental principle behind the operation of semi-automatic mode in a fully automatic capable weapon.

The disconnect and the trigger both pivot on the trigger pin 31 (see FIGS. 1-3). Edge 42 engages the hammer in the fully reset position and when the trigger is depressed, thus presenting this edge in interference with the corresponding surface on the hammer. When the selector is in full automatic mode, it contacts surface 43 on the disconnect to prevent motion of the disconnect, effectively removing or “disconnecting” it from its ability to engage the hammer. Since the disconnect cannot engage the hammer, the weapon will continue to cycle rounds until ammunition has been depleted or until the trigger is released. Notch 44 allows for clearance with the selector when the selector has been moved to the semi-automatic position. This allows the disconnect to move with the trigger as it is depressed, presenting the disconnect in interference with the hammer. A pocketed spring 45 acts on surface to rotate the disconnect counter-clockwise with respect to the trigger (see FIG. 8).

FIG. 8 shows the trigger and disconnect in section. The trigger 8 blocks the counter-clockwise rotation of the disconnect at point 46. Effectively the disconnect can move clockwise a small distance against the spring force to allow engagement with the hammer.

Carrier Sear

FIG. 9 shows the carrier sear 10, whose purpose is to hold the carrier in the rearward position. The carrier sear pivots about pivot pin 51 (see FIGS. 1-3) and engages a notch in the bottom of the carrier and holds it in the rearward position when the weapon is in automatic mode and the trigger is released. When the trigger is pulled, it cams the carrier sear to disengage it from the carrier and initiate the automatic cycle.

Surface 52 is cut away to allow retention of the pivot axis pin by means of a spring wire engaging a groove in the pin. Surface 53 sears with the carrier to interrupt the automatic cycle. When the trigger is depressed, this surface disengages from the carrier and the automatic cycle begins. Slot 54 houses and aligns the safety sear 11. Pocket 55 houses a spring that separates the safety sear from the carrier sear. Surface 56 is blocked by the selector when in safe mode to prevent any downward motion of the carrier sear, thus preventing forward movement of the carrier in open-bolt mode, and thus accidental preventing firing (in addition to the selector then also blocking movement of the trigger).

Safety Sear

FIGS. 10A and 10B are perspective views of the safety sear 11, and FIG. 11 shows the safety sear and carrier sear together in cross-section. The safety sear pivots about pivot pin 51, i.e. on the same pin and axis as the carrier sear, and holds the carrier in a rearward position in the event of incomplete charging action. This prevents a round from being chambered, since the point at which the safety sear can engage the carrier precedes the picking up of a new round or the subsequent engagement of the carrier sear. The carrier sear engages a notch in the bottom of the carrier and holds it in the rearward position when the weapon is in automatic mode and the trigger is released. When the trigger is pulled, it cams the carrier sear to disengage it from the carrier and initiate the automatic cycle.

Edge 62 sears with a notch in the bottom of the carrier. When the trigger is depressed it pushes against surface 63 to rotate the safety sear away from the carrier. The safety sear will travel a short distance until it hits the carrier sear, at which point both will continue to move as a pair away from the carrier, preventing either from engaging the carrier. Surface 64 is acted on by a pocketed spring 65 within the carrier sear to separate the two, moving the safety sear counter-clockwise with respect to the carrier sear. Surface 66 is engaged by the auto-disconnect in semi-automatic mode to capture both the safety sear and the carrier sear down and away from the carrier.

Auto-Disconnect

FIGS. 12A-12C show various views of the auto-disconnect 12, which pivots about auto-disconnect pin 71 and whose purpose is to hold the safety sear and carrier sear away from the carrier when the weapon is in semi-automatic mode. The auto-disconnect is free to engage the safety sear in semi-automatic mode. This occurs once the trigger is depressed and the safety sear over-travels the auto-disconnect, capturing it. At this point the carrier sear is moving with the safety sear as a single unit.

Surface 72 engages the safety sear as the safety sear over-travels the auto-disconnect. It prevents the safety sear and subsequently the carrier sear from rising under the influence of their respective springs. Groove 73 holds a spring wire that influences the safety sear in the counter-clockwise direction. Surface 74 is cammed by the selector when switched to automatic mode, to release the safety sear and carrier sear, allowing either of them to engage the carrier as conditions permit. Surface 75 is cut away to allow retention of the pivot axis pin by means of a spring wire engaging a groove in the pin.

Selector

FIGS. 13A and 13B show the selector 13, which pivots in hole 81 and whose purpose is to control the mode in which the firing mechanism operates. The operator moves the selector arm 82, sweeping it through a 90° arc with detents to select one of three specific operating modes: safe, semi-automatic or automatic. The selector accomplishes this by presenting material in interference or slots/grooves to allow movement of various components, as can be seen from FIGS. 14A-14D. There are several different slots of different shape and orientation along the body of the selector depending on which component it is interacting with. The arm 82 at one end of the body is the lever by which the operator selects the mode. There is another arm that attaches to the selector on the opposite end of the cylinder to retain it in the receiver of the firearm. This allows for ambidextrous manipulation of the selector. (Note that there is only one selector arm 82 shown in the drawings. The second is attached during assembly of the firearm, to retain the selector in the receiver and to provide for operation from either side of the weapon.) A portion 83 of the cam track interfaces with the auto-disconnect in safe mode. This ensures that the auto-disconnect is cammed out of engagement with the safety sear and allows it to rise and the selector to rotate into the safe position. Recess 84 allows the auto-disconnect to be moved by its spring to engage the safety sear, thus capturing it in semi-automatic mode. Surface 85, like surface 83, ensures that the carrier and safety sear can rise to engage the carrier in automatic mode. Surfaces 86 are both positioned to interfere with motion of both the trigger and the carrier sear when the selector is in the safe position. Conversely gap 87 allows motion of the carrier sear, allowing the trigger to be pulled.

Closed-Bolt Operation

This section describes how the invention operates in a manner analogous to a traditional closed-bolt weapon, i.e. when in closed-bolt mode.

When a self-loading weapon cycles, there are many moving parts that interact with each other to ensure that the firing mechanism is reset and the next available round of ammunition is loaded and ready to be fired. When a weapon is firing on fully automatic, this cycle continues repeatedly as long as the trigger is pulled until the source of ammunition has been depleted. The energy for all of these actions comes from expanding gases tapped from the barrel of the gun when a round is fired.

The cycle will stop when interrupted, either by the operator releasing the trigger or, in the case of a semi-automatic firearm, after only one round despite maintaining a depressed trigger. It is important to understand that the cycle is still ready to continue in either case, as long as ammunition is present, when the operator again depresses the trigger.

The difference between closed-bolt and open-bolt operation is defined by the position of the carrier and bolt when the cycle is interrupted. In a closed-bolt system the interruption occurs when the carrier is in the forward position and the bolt is locked with the barrel and a round is in the chamber. When the trigger is pulled the only internal moving parts are the trigger and the released hammer as it strikes the firing pin. This explains why closed-bolt operation is inherently more accurate, since the number of moving parts prior to the initiation of the round is minimized.

FIG. 15 shows the mechanism in its closed-bolt home position, with the trigger 8, the selector 13, the disconnect 9, the hammer 7, the auto-sear 6, the firing pin 90, and the carrier 5. In this position, the weapon has been cocked and is ready to fire. The firing mechanism has been reset and there would be a round in the chamber.

FIG. 16 shows Step 1 of the operating cycle, which is immediately after the trigger 8 has been pulled. The hammer 7 is just starting to move counter-clockwise under the force of its spring. Note that since the carrier 5 is in the forward position, the auto-sear 6 is disengaged from the hammer, allowing it to move. (In semi-automatic mode the safety sear serves as a safety device, preventing the hammer from striking the firing pin if the carrier is not fully forward and thus the bolt being locked. It is a potentially dangerous situation if a round is fired without the bolt being locked.)

FIG. 17 shows Step 2 of the operating cycle. The hammer 7 strikes the firing pin 90, initiating the round.

FIG. 18 shows Step 3 of the operating cycle. The carrier 5 travels rearward as the round is fired. Notice that the trigger 8 is still depressed and thus the disconnect 9 latches onto the hammer 7 as it is pushed back by the carrier. In addition, since the carrier is positioned to the rear, the auto-sear 6 has now re-engaged the hammer as well.

FIG. 19 shows Step 4 of the operating cycle. The trigger 8 remains depressed and the carrier 5 has traveled forward, loading another round. The disconnect 9 prevents the hammer 7 from moving once the auto-sear 6 is disengaged by the carrier 5. The disconnect has thus interrupted the cycle, allowing only one round to be fired.

From the Step 4 position, Step 5 is back to the home position of FIG. 15 again As the trigger 8 is released, its leading edge engages the notch 24 (see FIG. 5B) in the hammer prior to the disconnect releasing the hammer. The mechanism is now once again ready to fire another single round for each depression of the trigger.

Open-Bolt Operation

This section describes how the invention operates in a manner analogous to a traditional open-bolt weapon, i.e. in automatic mode.

As explained above, the difference between closed-bolt and open-bolt operation is defined by the position of the carrier and bolt when the firing cycle is interrupted. In an open-bolt system the carrier is in the rearward position. When the trigger is pulled the carrier is released and travels forward. As the carrier travels forward it pushes a round into the chamber (something the closed-bolt cycle had accomplished before pulling the trigger). This is beneficial in high rates of fire since the rounds are not exposed to the heat of the chamber except directly before the firing pin initiates the round. Keeping a round out of a hot chamber prevents the possibility of cook-off, as explained above. The downside of open-bolt operation is that there is a significant movement of mass within the firearm between the time the trigger is pulled and when the round is actually fired. As a result the point of aim may move before the round is fired, thus making it inherently less accurate. In situations of fully automatic fire, this level of inaccuracy is overwhelmed by the repeated motion of the carrier and recoil of full automatic fire and is thus considered acceptable.

FIG. 20 shows the mechanism in the home position of the operating cycle, in which the weapon has been cocked and is ready to fire. The firing mechanism is reset. The difference from the closed-bolt cycle is that the carrier 5 is to the rear and no round is loaded in the chamber. As will be explained later below, the carrier does not move to the rear as soon as the selector 13 is switched from semi-automatic to automatic. Instead, it remains forward until the first round is fired.

FIG. 21 shows Step 1 of the operating cycle. As the trigger 8 is depressed, it cams the carrier sear 10 out of engagement with the carrier 5. The carrier is just beginning its forward motion, propelled by a typical recoil spring (not shown). In addition, the trigger disengages from the hammer 7. Note that at this point the over-travel of the carrier and the engagement of the auto-sear are preventing the hammer from moving.

FIG. 22 shows Step 2 of the operating cycle. As the carrier 5 travels forward, the bolt strips a round from the magazine (conventional and therefore not shown), loading it into the chamber and subsequently locking with the barrel. When the carrier is fully forward, it disengages the auto-sear 6 from the hammer 7.

FIG. 23 shows Step 3 of the operating cycle. The hammer 7 rotates forward under the force of its spring 22 (not shown in this view; see FIG. 2) and strikes the firing pin 90, initiating the round.

FIG. 24 shows Step 4 of the operating cycle. The carrier 5 travels to the rear, resetting the trigger mechanism. Note that the auto-sear 6 has re-engaged the hammer 7. At this point if the trigger 8 remains pulled, the cycle will go to Step 2 and continue to cycle from Step 2 to Step 4 until all ammunition has been exhausted or the trigger is released.

From the FIG. 24 position, Step 5 of the operating cycle is back to the FIG. 20 home position. When the trigger is released, the carrier sear interrupts the cycle and the mechanism stops in the home position. Otherwise, the carrier sear remains in the FIG. 21 position, and the weapon fires again as soon as the carrier is fully forward to disengage the auto-sear and allow the hammer to fly forward.

Integration of Open-Bolt and Closed-Bolt Operation Introduction

It is a particular advantage of aspects of the invention that the firearm can operate as an open-bolt firearm in fully automatic mode, or as a closed-bolt firearm in semi-automatic mode. The integration of the two different operating modes and the operating logic will now be described.

In the invention, the bolt position change is effected after the first round has been fired, subsequent to the mode change. Thus there is no motion of the carrier upon mode selection, either from closed bolt to open bolt, or vice versa.

The dual-mode operation is achieved primarily by virtue of the auto-disconnect 12 and its interaction with the safety sear 11. It should be noted that the safety sear provides a protective function that prevents a round from being chambered if the carrier sear 10 has not engaged the carrier 5.

Note that the operative surfaces of the safety sear could be integrated into the carrier sear, i.e. in a single piece, if for some reason the presence of the safety sear is considered obsolete or redundant. However, the preferred embodiment advantageously contemplates having these as two separate components.

Safety Sear Function

The safety sear is free to rise, separating from the carrier sear, when it is not being acted on by the trigger. This happens due to a pocketed spring between the two, as described above. The purpose of the safety sear is to prevent possible accidental chambering of a round if an operator pulls back on the charging handle of the firearm, but not quite far enough back to engage the carrier sear. The carrier assembly may have moved back far enough to engage the next round in the magazine, so that if the operator releases the charging handle, a round will be chambered and the bolt will close, despite the selector being set to the open-bolt mode. If this occurs after a prolonged high rate of fire, the chamber of the weapon will be hot and the potential for cook-off exists—something the open-bolt mechanism is designed to avoid. The safety sear, however, being shorter, can engage the carrier to hold it back even if the carrier is not pulled back far enough to engage the carrier sear.

From the stage shown in FIG. 20, the firearm will fire in automatic mode when the trigger is pulled and will cycle normally. The safety sear is never presented to the notch in the carrier. Since the safety sear directly interacts with the trigger and subsequently sweeps the carrier sear away from the carrier, the safety sear is removed from any possible interference before the cycle starts.

In semi-automatic operation, the auto-disconnect 12 engages the lower arm of the safety sear 11, whereas in automatic operation, the auto-disconnect has been rotated by the selector and thus cannot engage the safety sear. The surface 35 on the trigger raises to cam the safety sear in this area when the trigger is depressed, so that it can be engaged by the auto-disconnect when in semi-automatic operation.

Automatic to Semi-Automatic Transition

In FIG. 20, the firearm is in the automatic home position, in which the auto-disconnect remains cammed out of the way by the selector Note that the carrier is to the rear in the open-bolt configuration.

In FIG. 25, when the selector 13 is moved to the semi-automatic mode (closed-bolt operation), the auto-disconnect 12 is allowed to rotate counter-clockwise under the force of its spring to be in position to be ready to interfere with the safety sear 11.

In FIG. 26, when the trigger 8 is depressed, initiating a semi-automatic cycle, the safety sear 11 snaps past the auto-disconnect 12.

In FIG. 27, the safety sear 11 and carrier sear 10 are held down and away from the carrier 5 even when the trigger 8 is released, after one round has been fired. Note that now the firearm is in the closed-bolt configuration.

The difference between this and a regular semi-automatic cycle is the initial movement and subsequent capture of the safety sear and carrier sear, effectively removing them from participating in the action thereafter.

Semi-Automatic to Automatic Transition

In FIG. 27, the firearm is in semi-automatic mode. The selector has not yet been switched to the automatic mode (open-bolt). Note that the carrier 5 is forward, in the closed-bolt configuration.

In FIG. 28, the selector 13 has been moved to the automatic mode. Note the movement of the auto-disconnect 12 and subsequent release of the safety sear 11 and carrier sear 10 combination. It should be stressed that the arm of the auto-disconnect where it contacts the selector does not touch the carrier sear. The motion of the carrier sear and safety sear are only a result of their spring driving them upwards once the auto-disconnect has released them

FIG. 29 is part way through the automatic cycle, with the trigger 8 remaining depressed. The firearm will continue to cycle in this state until the trigger is released or ammunition is depleted.

From the FIG. 29 position, as the trigger 8 is released, the firearm returns to the automatic (open-bolt) home position of FIG. 20.

Summary

It can thus be seen that the invention advantageously allows the weapon to be easily switched between closed-bolt semi-automatic operation, and open-bolt automatic operation, without the disadvantage of noise or significant mechanical movement at the time of changing the mode of operation. The carrier 5 does not move until the first round is fired after operating the selector 13 to change the mode.

The above description is of a preferred embodiment, by way of example only. Those knowledgeable in the field of the invention will understand that there are many possible variations within the scope of the invention. The scope of the invention therefore is not limited to the above description, but instead is defined by the following claims. 

1. A trigger mechanism for a firearm capable of both an open-bolt automatic mode of operation where a carrier spring-biased towards a forward firing position is normally held back from said forward firing position in a rearward position, and a closed-bolt semi-automatic mode of operation where the carrier is normally released into said forward firing position, said trigger mechanism comprising a selector operable to switch between said modes, said mechanism retaining an open-bolt configuration on being switched via said selector from open-bolt semi-automatic mode to closed-bolt mode automatic mode, and retaining a closed-bolt configuration on being switched via said selector from closed-bolt semi-automatic mode to open-bolt automatic mode, until a first round is fired after being so switched.
 2. A trigger mechanism as in claim 1, further comprising a carrier sear biased to engage said carrier to hold said carrier in said rearward position in said open-bolt automatic mode, said trigger mechanism including an auto-disconnect operable via said selector, said auto-disconnect positioned to block said carrier sear from moving into engagement with said carrier when in closed-bolt semi-automatic mode, thereby allowing said carrier to move to said forward firing position, and positioned away from said carrier sear when in open-bolt automatic mode, thereby allowing said carrier sear to engage said carrier.
 3. A trigger mechanism as in claim 2, having a trigger which when pulled contacts a surface of said carrier sear to move said carrier sear out of engagement with said carrier.
 4. A trigger mechanism as in claim 3, further comprising a disconnect spring-biased from said trigger to engage a hammer after firing of the firearm in said semi-automatic mode when said hammer is cocked by contact from rearward motion of said carrier, said trigger having a sear portion to engage a trigger sear on said hammer when said trigger is released, said disconnect then releasing said hammer; said selector blocking said disconnect from moving to engage said hammer when in said automatic mode.
 5. A trigger mechanism as in claim 1, further comprising an auto-sear, biased to engage a hammer to prevent said hammer from rotating to impact a firing pin, said auto-sear having a portion thereof positioned to be contacted by said carrier as said carrier arrives at said forward firing position, such contact moving said auto-sear out of engagement with said hammer, thereby permitting said hammer to rotate to impact said firing pin unless otherwise restrained, for example by a trigger sear.
 6. A trigger mechanism as in claim 2, further comprising an auto-sear, biased to engage a hammer to prevent said hammer from rotating to impact a firing pin, said auto-sear having a portion thereof positioned to be contacted by said carrier as said carrier arrives at said forward firing position, such contact moving said auto-sear out of engagement with said hammer, thereby permitting said hammer to rotate to impact said firing pin unless otherwise restrained, for example by a trigger sear.
 7. A trigger mechanism as in claim 3, further comprising an auto-sear, biased to engage a hammer to prevent said hammer from rotating to impact a firing pin, said auto-sear having a portion thereof positioned to be contacted by said carrier as said carrier arrives at said forward firing position, such contact moving said auto-sear out of engagement with said hammer, thereby permitting said hammer to rotate to impact said firing pin unless otherwise restrained, for example by a trigger sear.
 8. A trigger mechanism as in claim 4, further comprising an auto-sear, biased to engage said hammer to prevent said hammer from rotating to impact a firing pin, said auto-sear having a portion thereof positioned to be contacted by said carrier as said carrier arrives at said forward firing position, such contact moving said auto-sear out of engagement with said hammer, thereby permitting said hammer to rotate to impact said firing pin unless otherwise restrained, for example by a trigger sear. 